Industrial production of acrylic acid is at present carried out by vapour phase catalytic oxidation of acrolein. All attempts to improve this process have hitherto related to the development of catalysts giving the highest possible conversion of acrolein and the highest possible selectivity for the desired acrylic acid.
Thus, French Patent No. 2 222 349 describes a catalyst for the preparation of acrylic acid by vapour phase catalytic oxidation of acrolein using a gas containing molecular oxygen, this catalyst including a catalytic oxide on an inert porous support, this catalytic oxide having the following metal composition: EQU Mo.sub.12 V.sub.2-14 Z.sub.0.1-6 W.sub.0-12 Cu.sub.0-6
Z being at least one of Be, Mg, Ca, Ba and Sr, and at least one of W and Cu being always present.
This catalyst can be prepared by adding a support (powdered material or .alpha.-alumina, silicon carbide or similar beads) to an aqueous solution in which compounds of the various catalyst elements are dissolved, evaporating the aqueous solution to dryness to deposit the catalyst elements on the support and calcining the dried product between 300 and 800.degree. C.